In a room of 30 kids, what are the odds two of them share a birthday?
At the next class party, ask two different questions before anyone checks dates: does someone match one chosen person, or does any pair match?
Talk about it
- Name the two different birthday questions before you make a prediction.
- Add one person to a small group: how many one-person spokes and all-pair links are new?
- Where else could many small chances combine into a surprising collision?